PURPOSE: To lessen a degree of superheat of suction gas and improve volumetric efficiency in a compound compressor for compression of refrigerating working gas by providing heat insulating spaces between suction chambers and delivery chambers partitioned by a head cover therebetween.

CONSTITUTION: A low-pressure stage side heat insulating space 22 is formed between a low-pressure stage side bulkhead 21 partitioning upper parts of a first and a second cylinders into inner and outer two chambers and a low-pressure stage delivery wall 25 partitioning off a low-pressure stage delivery chamber 15, on the inside of a head cover 6, and air is sealed therein. A high-pressure stage side bulkhead 23 partitioning an upper part of a third cylinder into the inside and the outside is formed, and a high-pressure stage delivery chamber 19 is formed on the inside surrounded with the bulkhead 23. Further, a high-pressure stage side heat insulating space 24 is formed between the high-pressure stage side bulkhead 23 and a wall 26 of the high-pressure stage delivery chamber 19, and air is enclosed therein and sealed with a gasket. With this constitution, respective heat transfers to the low-pressure stage delivery chamber 15 and the high-pressure stage delivery chamber 19 are made small by the low-pressure stage side heat insulating space 22 and the high-pressure stage side heat insulating space 24.